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author William Astle <lost@l-w.ca>
date Wed, 17 Aug 2022 17:05:01 -0600
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><H1
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><A
NAME="AEN942"
>4.3. Linking Scripts</A
></H1
><P
>A linker script is used to instruct the linker about how to assemble the
various sections into a completed binary. It consists of a series of
directives which are considered in the order they are encountered.</P
><P
>The sections will appear in the resulting binary in the order they are
specified in the script file. If a referenced section is not found, the linker will behave as though the
section did exist but had a zero size, no relocations, and no exports.
A section should only be referenced once. Any subsequent references will have
an undefined effect.</P
><P
>All numbers are in linking scripts are specified in hexadecimal. All directives
are case sensitive although the hexadecimal numbers are not.</P
><P
>A section name can be specified as a "*", then any section not
already matched by the script will be matched. The "*" can be followed
by a comma and a flag to narrow the section down slightly, also.
If the flag is "!bss", then any section that is not flagged as a bss section
will be matched. If the flag is "bss", then any section that is flagged as
bss will be matched.</P
><P
>The following directives are understood in a linker script.</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
>sectopt <CODE
CLASS="PARAMETER"
>section</CODE
> padafter <CODE
CLASS="PARAMETER"
>byte,...</CODE
></DT
><DD
><P
>&#13;This will cause the linker to append the specified list of byte values
(specified in hexadecimal separated by commas) to the end of the named
section.  This is done once all instances of the specified section are
collected together.  This has no effect if the specified section does not
appear anywhere in any of the objects specified for linking. &#13;</P
><P
>&#13;If code depends on the presence of this padding somewhere, it is sufficient
to include an empty section of the specified name in the object that depends
on it.&#13;</P
></DD
><DT
>define basesympat <CODE
CLASS="PARAMETER"
>string</CODE
></DT
><DD
><P
>&#13;This causes the linker to define a symbol for the ultimate base address of
each section using the pattern specified by <CODE
CLASS="PARAMETER"
>string</CODE
>. 
In the string, %s can appear exactly once and will be replaced with the
section name.  The base address is calculated after all instances of each
section have been collapsed together.&#13;</P
><P
>&#13;It should be noted that if none of the objects to be linked contains a
particular section name, there will be no base symbol defined for it, even
if it is listed explicitly in the link script.  If code depends on the
presence of these symbols, it is sufficient to include an empty section of
the specified name in the object that depends on it.&#13;</P
><P
>  If the pattern resolves to the same string for multiple
sections, the results are undefined.&#13;</P
></DD
><DT
>define lensympat <CODE
CLASS="PARAMETER"
>string</CODE
></DT
><DD
><P
>&#13;This causes the linker to define a symbol for the ultimate length of each
section using the pattern specified by <CODE
CLASS="PARAMETER"
>string</CODE
>.  In
the string, %s can appear exactly once and will be replaced with the section
name.  The length is calculated after all instances of a section have been
collapsed together.&#13;</P
><P
>&#13;It should be noted that if none of the objects to be linked contains a
particular section name, there will be no length symbol defined for it, even
if it is listed explicitly in the link script.  If code depends on the
presence of these symbols, it is sufficient to include an empty section of
the specified name in the object that depends on it.&#13;</P
><P
>If the pattern resolves to the same string for multiple
sections, the results are undefined.&#13;</P
></DD
><DT
>section <CODE
CLASS="PARAMETER"
>name</CODE
> load <CODE
CLASS="PARAMETER"
>addr</CODE
></DT
><DD
><P
>&#13;This causes the section <CODE
CLASS="PARAMETER"
>name</CODE
> to load at
<CODE
CLASS="PARAMETER"
>addr</CODE
>. For the raw target, only one "load at" entry is
allowed for non-bss sections and it must be the first one. For raw targets,
it affects the addresses the linker assigns to symbols but has no other
affect on the output. bss sections may all have separate load addresses but
since they will not appear in the binary anyway, this is okay.</P
><P
>For the decb target, each "load" entry will cause a new "block" to be
output to the binary which will contain the load address. It is legal for
sections to overlap in this manner - the linker assumes the loader will sort
everything out.</P
></DD
><DT
>section <CODE
CLASS="PARAMETER"
>name</CODE
> high <CODE
CLASS="PARAMETER"
>addr</CODE
></DT
><DD
><P
>&#13;This causes the section <CODE
CLASS="PARAMETER"
>name</CODE
> to load with its end
address just below <CODE
CLASS="PARAMETER"
>addr</CODE
>.  Subsequent sections are
loaded at progressively lower addresses.  This may lead to inefficient file
encoding for some targets.  As of this writing, it will also almost
certainly do the wrong thing for a raw target.&#13;</P
><P
>&#13;This is useful for aligning a block of code with high memory.  As an
example, if the total size of a section is $100 bytes and a high address of
$FE00 is specified, the section will actually load at $FD00.&#13;</P
></DD
><DT
>section <CODE
CLASS="PARAMETER"
>name</CODE
></DT
><DD
><P
>&#13;This will cause the section <CODE
CLASS="PARAMETER"
>name</CODE
> to load after the previously listed
section.</P
></DD
><DT
>entry <CODE
CLASS="PARAMETER"
>addr or sym</CODE
></DT
><DD
><P
>This will cause the execution address (entry point) to be the address
specified (in hex) or the specified symbol name. The symbol name must
match a symbol that is exported by one of the object files being linked.
This has no effect for targets that do not encode the entry point into the
resulting file. If not specified, the entry point is assumed to be address 0
which is probably not what you want. The default link scripts for targets
that support this directive automatically starts at the beginning of the
first section (usually "init" or "code") that is emitted in the binary.</P
><P
>Note that if you use a numeric value here, you will need to ensure
it starts with a digit. That may mean adding a leading zero.</P
></DD
><DT
>pad <CODE
CLASS="PARAMETER"
>size</CODE
></DT
><DD
><P
>This will cause the output file to be padded with NUL bytes to be exactly
<CODE
CLASS="PARAMETER"
>size</CODE
> bytes in length. This only makes sense for a raw target.</P
></DD
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